Remove unused wrapper methods

There are some wrapper methods in base.py of messaging tests but
get_single_message and get_multiple_messages are not used at all.
These methods just call client methods without any special behaviors
and they seems redundant. So this patch removes them.

Change-Id: I596a1089c4bfb66b7daf1b27779208920d251e63
diff --git a/tempest/api/messaging/base.py b/tempest/api/messaging/base.py
index 2ddc3fc..34ac860 100644
--- a/tempest/api/messaging/base.py
+++ b/tempest/api/messaging/base.py
@@ -116,20 +116,6 @@
         return resp, body
 
     @classmethod
-    def get_single_message(cls, message_uri):
-        """Wrapper utility that gets a single message."""
-        resp, body = cls.client.show_single_message(message_uri)
-
-        return resp, body
-
-    @classmethod
-    def get_multiple_messages(cls, message_uri):
-        """Wrapper utility that gets multiple messages."""
-        resp, body = cls.client.show_multiple_messages(message_uri)
-
-        return resp, body
-
-    @classmethod
     def delete_messages(cls, message_uri):
         """Wrapper utility that deletes messages."""
         resp, body = cls.client.delete_messages(message_uri)